The propagation of inverted Neel wall sections instead of magnetic bubbles in a serial access memory system was proposed by L. J. Schwee, et al, in the publication "Proposal on Cross-Tie Wall and Bloch-Line Propagation in Thin Magnetic Films," IEEE Transactions on Magnetics, MAG 8, No. 3, Pages 405-407, September, 1972. Such a memory system utilizes a ferromagnetic film of 81% Ni-19% Fe approximately 350 Angstroms (A) thick in which cross-tie walls can be changed to Neel walls and Neel walls can be changed to cross-tie walls by applying appropriate fields. Associated with the cross-tie wall is a section of inverted Neel wall that is bounded by a cross-tie on one end and a Bloch-line on the other end.
In such a cross-tie wall memory system, information is entered at one end of the serial access memory system by the generation of an inverted Neel wall section, bounded by a cross-tie on one side and a Bloch-line on the other side, that is representative of a stored binary 1, and a non-inverted Neel wall section, i.e., that absence of a cross-tie, Bloch-line pair, that is representative of a stored binary 0. The inverted Neel wall section is moved or propagated along the cross-tie wall by the successive generation and then the selective annihilation of inverted Neel wall sections at successive memory cells along the cross-tie wall.
In the D. S. Lo, et al, U.S. Pat. No. 3,906,466 there is disclosed a propagation circuit for the transfer of inverted Neel wall sections at successive memory cells along the cross-tie wall. In the L. J. Schwee U.S. Pat. No. 3,868,660 and in the publication "Cross-Tie Memory Simplified by the Use of Serrated Strips," L. J. Schwee, et al, AIP Conference Proceedings, No. 29, 21st Annual Conference on Magnetism and Magnetic Materials, 1975, published April, 1976, Pages 624-625, there have been published some more recent results of the further development of cross-tie wall memory systems.
In such prior art cross-tie wall memory systems, the magnetic film that functions as the storage medium has the property of uniaxial anisotropy provided by its easy axis induced magnetic field, which easy axis is created in the magnetic film in its generation during the vapor deposition process. This easy axis provides a magnetic field induced anisotropy which constrains the generation of the cross-tie wall along and parallel to the easy axis. In the above L. J. Schwee, et al, publication there are proposed serrated strips of Permalloy film, about 350 A in thickness and 10 microns (.mu.m) in width, which serrated strips are etched from a planar layer of the magnetic material so that the strips are aligned along the easy axis of the film. After an external magnetic field is applied normal to the film strip, i.e., transverse the easy axis of the film, the magnetization along the opposing serrated edges rotates back to the nearest direction that is parallel to the edge. This generates two large domains that are separated by a domain, or cross-tie, wall that is formed along the centerline of the strip. Cross-ties are formed at the necks of the serrated edges while Bloch-lines are formed in the potential wells between adjacent necks.
This serrated strip configuration, because of the contour of the opposing edges of the strip, provides the means whereby the cross-tie, Bloch-line pairs are structured at predetermined memory sections along the strip. However, such serrated strips, because of their sharp, angular design, are susceptible to the generation of undesirable magnetic domain walls that inhibit the propagation of the cross-tie, Bloch-line pairs along the data track. Accordingly, it is desirable that there be provided strips of Permalloy that have an edge conformation that structures the positions of cross-tie, Bloch-line pairs along the data track defining strip while avoiding the generation of undesirable magnetic domain walls as does the serrated strip of L. J. Schwee, et al.
In the co-pending patent application of L. H. Johnson, et al. Ser. No. 756,223, filed Jan. 3, 1977, now U.S. Pat. No. 4,075,612, there is disclosed the design of the edge contour of a film strip of, e.g., Permalloy film of approximately 350 A in thickness and approximately 10 .mu.m in width. The edge contours are mirror images, one of the other, of asymmetrical, repetitive patterns of rounded edge portions. The edge contour of each opposing pair of rounded edge portions is substantially in alignment with the natural contour of the magnetization that is oriented around a Bloch-line, which Bloch-line is positioned along the cross-tie wall that is oriented along the geometric centerline of the film strip. The neck or narrowest point of the edge contour between adjacent rounded edge portions functions to structure the static or rest position of the associated cross-tie of the cross-tie, Bloch-line pair, which rest position is also situated upon the anisotropic easy axis which is aligned along the geometric centerline of the film strip.
In the co-pending patent application of M. C. Paul, et al, Ser. No. 756,224, filed Jan. 3, 1977, there is disclosed a novel cross-tie wall memory system and in particular a data track therefor that is formed of a strip of magnetic material having substantially zero uniaxial anisotropy. This is achieved by rotating the substrate during deposition. The data-track-defining-strip of isotropic magnetic film utilizes its shape, i.e., its edge contour induced, anisotropy to constrain the cross-tie wall within the planar contour of the film strip. Accordingly, the cross-tie wall is constrained to follow the path defined by the magnetic film strip, which path may be configured into a major loop, minor loop configuration for large capacity memory storage.